Method of bonding semiconductor substrate and MEMS device

ABSTRACT

A method of bonding a semiconductor substrate has a step of pressurizing and heating to bond a substrate  11  with a substrate  12  by eutectic bonding in a state that an aluminum containing layer  31  and a germanium layer  32  between a bonding section  30   a  of the substrate  11  and a bonding section  30   b  of the substrate  21  are overlaid and an outer end  32   a  of the germanium layer  32  is receded inward with respect to an outer end  31   a  of the aluminum containing layer  31.

TECHNICAL FIELD

The invention relates to a method of bonding by eutectic bonding of twosemiconductor substrates and a MEMS device formed by the same.

BACKGROUND ART

As a bonding method of these kinds of semiconductor substrates, a methodhas been known in which a silicon wafer formed with a MEMS structure hasa germanium layer and a silicon wafer formed with integrated circuitshas an aluminum containing layer, the germanium layer and the aluminumcontaining layer are faced to each other to be pressurized and heated,and an eutectic alloy made of the germanium and aluminum fixed to eachother is formed (Patent Document 1).

-   [Patent Document 1] U.S. Pat. No. 7,442,570

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

In such a bonding method, in a case that the germanium layer and thealuminum containing layer are film-formed on a whole bonding surface ofthe semiconductor substrates, the eutectic alloy made of the germaniumand the aluminum might be formed to be pressed out from the bondingsurface by the pressurization. In other words, in this case, theeutectic alloy formed to be pressed out might be conducted to anelectrode formed around the bonding surface of the semiconductorsubstrate, and there arises a problem such that a device is defective,making productivity lower.

In view of the foregoing problem, it is an object of the invention toprovide a method of bonding a semiconductor substrate without letting aneutectic alloy press out from a bonding surface in eutectic bonding andto provide a MEMS device formed by the same.

Means for Solving the Problems

According to one aspect of the invention, there is provided a method ofbonding a semiconductor substrate in which a first semiconductorsubstrate is bonded with a second semiconductor substrate by eutecticbonding with pressurization and heating, an aluminum containing layerprimarily made of aluminum and a germanium layer in an overlaid statebeing interposed between a bonding surface of the first semiconductorsubstrate and a bonding surface of the second semiconductor substrate.The method has a step of receding an outer end of the germanium layerinward with respect to an outer end of the aluminum containing layer asto the aluminum containing layer and the germanium layer in the overlaidstate.

According to the structure above, since the outer end of the germaniumlayer is receded inward with respect to the outer end of the aluminumcontaining layer, a formed eutectic alloy does not protrude from thebonding surface even if the eutectic alloy in a melting state by thepressurization spreads to an outside. Therefore, undesirable conductionto an electrode can be avoided and productivity of the device can beimproved. The length from the outer end of the aluminum containing layerto the receded outer end of the germanium layer is preferably equal toor less than 20 μm. Further, the aluminum containing layer and thegermanium layer may be film-formed on either the first semiconductorsubstrate or the second semiconductor substrate. Still further, thealuminum containing layer and the germanium layer may be film-formed ona bonding surface of a same semiconductor substrate or on bondingsurfaces of different semiconductor substrates.

In this case, it is preferable that heating temperature and heating timeof the pressurization and heating be controlled for alloying thegermanium layer and the aluminum containing layer by eutectic bondingexcept an outer end portion of the aluminum containing layer.

According to the structure above, it is possible to control an areawhere the eutectic alloy is formed accurately, and to efficiently avoidthat the formed eutectic alloy protrudes from the substrates.

In these cases, it is preferable that the aluminum containing layer andthe germanium layer be film-formed on either the first semiconductorsubstrate or the second semiconductor substrate.

According to the structure above, since a metal film does not need to befilm-formed on the other semiconductor substrate, a film formationprocess before bonding the semiconductor substrate can be omitted,thereby a bonding process can be simplified.

In this case, it is preferable that the aluminum containing layer befilm-formed in a ring shape in planar view as having predeterminedwidth, and the germanium layer have one or more strip layer sectionsfilm-formed in a ring shape in planar view on the aluminum containinglayer.

According to the structure above, since the eutectic alloy is formedconsecutively in a direction orthogonal to an inner/outer direction ofthe semiconductor substrate, it is possible to bond the semiconductorsubstrate with high sealing characteristics.

Further in this case, it is preferable that the aluminum containinglayer be film-formed in a ring shape in planar view as havingpredetermined width, and the germanium layer have a strip layer sectionfilm-formed in a ring shape in planar view and a plurality of branchlayer sections branched from the strip layer section on the aluminumcontaining layer.

According to the structure above, since a total extension of a contactend of the germanium layer to the aluminum containing layer can belonger, the eutectic alloy formed by the heating and pressurizationtends to fix on the first semiconductor substrate and bonding with highbonding strength can be performed.

In these cases, it is preferable that the aluminum containing layer andthe germanium layer be film-formed on the second semiconductor substrateand a pit be formed on the bonding surface of the first semiconductorsubstrate, in which a eutectic alloy generated by the pressurization andheating fills.

According to the structure above, the eutectic alloy in the meltingstate formed in a vacuum by the heating and the pressurization fills inthe pit by capillary phenomenon. This leads the eutectic alloy to spreadin the pit thoroughly, thereby, since the eutectic alloy layer is formedto bite in the first semiconductor substrate, bonding strength of thebonding section can be increased. The pit formed in the firstsemiconductor substrate may be a plurality of apertures formedintermittently or a slit-like groove formed consecutively.

According to the other aspect of the invention, there is provided a MEMSdevice bonded by the above bonding method of the semiconductorsubstrate. The first semiconductor substrate has a MEMS structure formedto be engraved at the bonding surface side thereof, and the secondsemiconductor substrate has an integrated circuit formed at the bondingsurface side to control the MEMS structure.

According to the structure, the substrates are bonded to avoidconduction to an undesired electrode, electric conducts of the MEMSstructure, the integrated circuit and an outer circuit are maintained,and the MEMS structure and the integrated circuit are packagedintegrally to protect against an outer environment such as moisture,temperature, dust and the like. Therefore, it is possible to provide aMEMS device having high precision.

Further in this case, it is preferable that the MEMS sensor above iseither one of an acceleration sensor, an angular velocity sensor, aninfrared ray sensor, a pressure sensor, a magnetic sensor and a sonicsensor.

According to the structure above, with the efficient package, it ispossible to provide the acceleration sensor, the angular velocitysensor, the infrared ray sensor, the pressure sensor, the magneticsensor and the sonic sensor having high precision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic appearance perspective views of a MEMSchip and a CMOS chip according to an embodiment.

FIG. 2 is a schematic perspective view of a MEMS device according to theembodiment.

FIGS. 3A and 3B are cross sectional views illustrating film formationarrangement of an aluminum containing layer and a germanium layeraccording to the embodiment.

FIG. 4 is a table describing film thickness of the aluminum containinglayer and the germanium layer, a weight ratio of the germanium layer tothe aluminum containing layer, and numeric values of a sealing ratio andshear strength (bonding strength) of a bonding section.

FIGS. 5A and 5B are graphs illustrating relationships among a weightratio of the germanium layer to the aluminum layer, the sealing ratioand the shear strength of the bonding section after eutectic bonding.

FIG. 6A is an elevation view and FIG. 6B is a cross sectional viewillustrating film formation arrangement of the aluminum containing layerand the germanium layer according to a first modification of theembodiment.

FIG. 7A is an elevation view and FIG. 7B is a cross sectional viewillustrating film formation arrangement of the aluminum containing layerand the germanium layer according to a second modification of theembodiment.

FIG. 8A is an elevation view and FIG. 8B is a cross sectional viewillustrating film formation arrangement of the aluminum containing layerand the germanium layer according to a third modification of theembodiment.

FIG. 9A is an elevation view and FIGS. 9B and 9C are cross sectionalviews illustrating film formation arrangement of the aluminum containinglayer and the germanium layer according to the other embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Referring to the accompanying drawings, a method of bonding asemiconductor and a MEMS device according to one embodiment of theinvention will be explained. In the method of bonding a semiconductorsubstrate according to the embodiment, a MEMS wafer having a number ofsensing sections is faced to a CMOS wafer having a number of integratedcircuits each of which controls each sensing section to bond by eutecticbonding via metal. In other words, in the invention, the formed MEMSsensor and the integrated circuits are formed in separate processes toface each other and are bonded by eutectic bonding. In the eutecticbonding, a wafer level package technology (WLP technology) is used, bywhich wafers are sealed collectively as they are, and then are cut offinto each chip.

A MEMS device according to the embodiment is fabricated by such eutecticbonding, and, for example, may be conceived as an acceleration sensor,an angular velocity sensor, an infrared ray sensor, a pressure sensor, amagnetic sensor and a sonic sensor.

FIG. 1A illustrates a piece in close-up of MEMS wafers (not illustrated)in which a plurality of sensing sections 12 are formed in a matrixshape. Hereinafter, a MEMS chip 10 as the piece will be explained forconvenience.

As illustrated, the MEMS chip 10 has a substrate 11 made of Silicon (Si)and a sensing section 12 formed at a center of the substrate 11 by microfabrication technology. The sensing section 12 is formed to be engravedat the center of the substrate 11 and is composed of elements of anacceleration sensor, an angular velocity sensor, an infrared ray sensor,a pressure sensor, a magnetic sensor, a sonic sensor or the like.Further, the substrate 11 has a ring-shaped bonding section 30 a in aplanar view which surrounds the sensing section 12. In the MEMS chip 10in the embodiment, the sensing section 12 and the bonding section 30 aare turned over to be upside down to face the CMOS chip 20 describedlater and the MEMS chip 10 is bonded with the CMOS chip 20. Then, thebonding section 30 a of the MEMS chip 10 is confronted with a bondingsection 30 b formed in the CMOS chip 20, and both are bonded by eutecticbonding via a metal layer film-formed on the bonding section 30 b. Thesubstrate 11 corresponds to a first semiconductor substrate and thesensing section 12 corresponds to a MEMS structure in claims.

FIG. 1B illustrates apiece in close-up from a CMOS wafer (notillustrated) in which a plurality of integrated circuits 22 are formedin a matrix shape. The CMOS chip 20 as the piece, similar to the MEMSchip 10, will be explained. The CMOS chip 20 has a substrate 21 made ofsilicon and the integrated circuit formed by micro fabricationtechnology (semiconductor fabrication technology) on the substrate 21.Further, the ring-shaped bonding section 30 b in a planar view isdisposed to surround a circuit central section 23 of the integratedcircuit 22 facing the sensing section 12 of the MEMS chip 10 at the timeof eutectic bonding. The integrated circuit 22 controls the sensingsection 12 of the MEMS chip 10 and is connected to input/output signallines from an outside.

Further, the integrated circuit 22 has aluminum wirings, and an aluminumcontaining layer 31 film-formed at the time of aluminum wiring formationbecomes a part of an eutectic alloy at the bonding. In other words, thebonding section 30 b of the CMOS chip 20 is formed in a same shapeapproximately in a planar view with the bonding section 30 a of the MEMSchip 10. At the bonding section 30 b of the CMOS chip 20, the aluminumcontaining layer 31 as the eutectic alloy is film-formed on thesubstrate 11 and a germanium layer 32 as the eutectic alloy isfilm-formed on the aluminum containing layer 31 (for example, filmformation by sputtering or vapor deposition technology). The substrate21 corresponds to a second semiconductor substrate and the bondingsection 30 b corresponds to a bonding section of the secondsemiconductor substrate.

FIG. 2 illustrates a MEMS device 1 formed by dicing or breaking the MEMSwafer and the CMOS wafer after the bonding (lamination bonding). Asillustrated, the MEMS device 1 is made up of the bonded MEMS chip 10 andthe CMOS chip 20 such that the sensing section 12 faces the circuitcentral section 23.

At the time of bonding, the MEMS chip 10 (MEMS wafer) and the CMOS chip20 (CMOS wafer) are confronted, are heated from both sides, that is,from the MEMS chip 10 side and the CMOS chip 20 side under vacuumenvironment and are pressurized from the MEMS chip 10 side. Thus, thegermanium layer film-formed at the bonding section 30 b of the CMOS chip20 develops eutectic reaction at a boundary surface with the aluminumcontaining layer 31, and an aluminum-germanium alloy (hereinafter,refereed as eutectic alloy) is formed. Especially, the eutectic alloy ina melting state is pressed against a silicon surface of the bondingsection 30 a to be welded by the pressurization from the MEMS chip 10side, and then, is fixed to be bonded solidly. Further, the eutecticbonding achieves electrical conduction between the substrates 11 and 21and high sealing characteristics. Heating temperature at the time ofbonding is preferably around 450° C. in consideration of heating damageto the sensing section 12 and the integrated circuit 22. Further, thepressurization at the time of bonding may be performed from CMOS chip 20side or from both the MEMS chip 10 side and the CMOS chip 20 side. Then,after the bonding, an individual MEMS device 1 is fabricated throughseparation process from a wafer to each chip.

Referring to FIGS. 3A and 3B, a film formation arrangement (filmformation pattern) of the aluminum containing layer 31 and the germaniumlayer 32 will be explained. FIGS. 3A and 3B are enlarged views of theA-A line cross section in FIG. 2. As illustrated in FIG. 3A, thealuminum containing layer 31 is evenly film-formed on the bondingsection 30 b of the CMOS chip 20 in a state before the eutectic bonding.Further, the germanium layer 32 on the aluminum containing layer 31 isfilm-formed such that an outer end 32 a of the germanium layer 32 isreceded inward with respect to an outer end 31 a of the aluminumcontaining layer 31. While, any metal layer is not film-formed at all onthe bonding section 30 a of the MEMS chip 10 and a silicon surface ofthe substrate 11 is barely formed. From this state, an eutectic alloylayer 33 is formed between the substrates 11 and 21 by the bondingmethod described above as illustrated in FIG. 3B, and the MEMS chip 10and the CMOS chip 20 are bonded by eutectic bonding. In the eutecticbonding of the embodiment, the pressurization and the heating iscontrolled appropriately, and a portion of the aluminum containing layer31 which is not in contact with the germanium layer 32 remains withouteutectic action (residual portion 34). In this case, the germanium layer32 is preferably film-formed thinner than the aluminum containing layer31 for the purpose of effective eutectic reaction.

Thus, in a case that a metal layer is not film-formed at the MEMS chip10 side before the bonding, a film formation process can be simplifiedafter forming the sensing section 12 and undesired effect such asdeformation, adhesion and breakage by film formation on a movablestructure of the sensing section 12 as a thin film can be avoided.Further, since the aluminum containing layer 31 utilizes aluminumwirings of the integrated circuit 22, metal film formation needed foractual bonding is only the germanium film formation on the bondingsection 30 b of the CMOS chip 20, thereby bonding process can besimplified. Still further, since the bonding section 30 is disposed tosurround the sensing section 12 and the circuit central section 23 andthe eutectic alloy layer 33 is formed in such away as to be orthogonalin an inner/outer direction of the facing MEMS chip 10 and the CMOS chip20, the MEMS chip 10 and the CMOS chip 20 can be bonded with highsealing characteristics and bonding strength. The aluminum containinglayer 31 and the germanium layer 32 may be film formed on either bondingsection of the MEMS chip 10 or of the CMOS chip 20, and they may befilm-formed on a bonding section of a same substrate or on bondingsections of different substrates.

Further, since the germanium layer 32 is film-formed such that the outerend 32 a of the germanium layer 32 is receded inward with respect to theouter end 31 a of the aluminum containing layer 31, the formed eutecticalloy is formed without being pressed out from the bonding section 30even if the eutectic alloy in the melting state expands to an outer sideby pressurization at the time of bonding, thereby undesired conductionto an electrode can be avoided and productivity (an yield rate) of adevice can be enhanced. Length from the outer end 31 a of the aluminumcontaining layer 31 to the outer end 32 a of the receded germanium layer32 is preferably equal to or less than 20 μm.

Referring to FIGS. 4 to 5B, a weight ratio of the germanium layer 32 tothe aluminum containing layer 31 at the time of bonding will beexplained. In the bonding method of the embodiment, heating temperatureand heating time as well as heating pressure is controlled for eutecticreaction between the whole germanium layer 32 and a part of the aluminumcontaining layer 31 in mutual bonding surfaces (see FIG. 3B). Inpractice, the weight ratio of the germanium layer 32 to the aluminumcontaining layer 31 is controlled by mainly a film thickness ratio ofthe germanium layer 32 to the aluminum containing layer 31. Therefore,the germanium layer 32 and the portion of the aluminum containing layer31 in contact therewith directly react by eutectic reaction, and theresidual portion of the aluminum containing layer 31 remains as it is(see FIG. 3B).

FIGS. 4 to 5B illustrate a test result of eutectic bonding in which filmthickness of the germanium layer 32 is changed arbitrary while filmthickness of the aluminum containing layer 31 is set fixedly (800 nm).FIG. 4 illustrates relationships among film thickness of the aluminumcontaining layer 31 and the germanium layer 32 film-formed before theeutectic bonding, a weight ratio of the germanium layer 32 to thealuminum containing layer 31, and a sealing ratio and shear strength(bonding strength) of the bonding section after the eutectic bonding.While, FIG. 5A is a graph of the weight ratio of the germanium layer 32to the aluminum containing layer 31 versus the sealing ratio of thebonding section after the eutectic bonding, and FIG. 5B is a graph ofthe weight ratio of the germanium layer 32 to the aluminum containinglayer 31 versus the shear strength (bonding strength) of the bondingsection after the eutectic bonding.

As illustrated in FIG. 5A, when the weight ratio of the germanium layer32 to the aluminum containing layer 31 is between 27 wt % and 57 wt %,the sealing ratio of the bonding section after the eutectic bonding isequal to or more than about 50%. Further, FIG. 5B illustrates that thebonding strength (shear strength) of the bonding section after theeutectic bonding is equal to or more than about 30 N when the weightratio of the germanium layer 32 is between 27 wt % and 52 wt %. Stillfurther, when the weight ratio of the germanium layer 32 is between 33wt % and 42 wt %, the sealing ratio is 100% and the shear strength(bonding strength) is between 41.6 N and 56.3 N (see FIG. 4). In short,it becomes apparent by the test result that the bonding is performedwith the highest sealing ratio and highest bonding strength when theeutectic bonding is performed by the method above with the weight ratioof the germanium layer 32 to the aluminum containing layer 31 as having33 wt % to 42 wt %. This also indicates that good eutectic bonding canbe obtained when the germanium layer 32 in the embodiment (filmthickness of the aluminum containing layer 31=800 nm) is film-formedbetween 200 nm and 300 nm thickness (see FIG. 4).

Referring to FIGS. 6A to 8B, a modification of the film formationarrangement of the aluminum containing layer 31 and the germanium layer32 according to the embodiment will be explained. FIG. 6A illustrates aportion of the bonding section 30 b of the CMOS chip 20 before theeutectic bonding, and FIG. 6B illustrates a cross section of the bondingsection 30 before the eutectic bonding (a first modification). Asillustrated, the aluminum containing layer 31 is evenly film-formed onthe bonding section 30 b of the CMOS chip 20 and the germanium layer 32is film-formed on the aluminum containing layer 31 in a plurality ofstrips shape. In short, the germanium layer 32 is made up of a pluralityof concentric strip layer sections 35 which have an identical shape.

In this kind of eutectic bonding, it has been known that the bondingstrength is high at the end portion of the germanium layer 32.Therefore, as the modification above, a total area of the end portion inthe germanium layer 32 (strip layer sections 35) can be increased byfilm-forming the germanium layer 32 as the strip layer sections 35, andstrong eutectic bonding can be achieved without increasing an area ofthe bonding section 30. Further, since the plurality of strip-shapedgermanium layers 32 are disposed to be orthogonal in the inner/outerdirection of the bonding section 30, the MEMS chip 10 and the CMOS chip20 can be bonded as having higher sealing characteristics and bondingstrength.

FIGS. 7A and 7B illustrate a second modification of the film formationarrangement of the aluminum containing layer 31 and the germanium layer32 according to the embodiment. As illustrated, in the film formationarrangement of the second modification, as the first modification, thealuminum containing layer 31 is evenly film-formed on the bondingsection 30 of the CMOS chip 20, and the germanium layer 32 film-formedon the aluminum containing layer 31 is integrally formed with a singlestrip layer section 35 and a plurality of branch layer sections 36. Thestrip layer section 35 is formed in a square ring-shape along thealuminum containing layer 31 at a center of the aluminum containinglayer 31 in a width direction. While, the plurality of branch layersections 36 are film-formed so as to branch from each section of thestrip layer section 35 to both sides at aright angle. Thus, a total areaof the end portion of the germanium layer 32 (strip layer section 35 andbranch layer sections 36) can be increased by forming the plurality ofbranch layer sections 36 (germanium layer 32) in a branch shape (fish'sbone shape), thereby strong eutectic bonding can be achieved.

FIGS. 8A and 8B illustrate a third modification of the film formationarrangement of the aluminum containing layer 31 and the germanium layer32. As illustrated, the film formation arrangement of the thirdmodification has a configuration in which the first modification iscombined with the second modification. In other words, in the thirdmodification, the aluminum containing layer 31 is evenly film-formed onthe bonding section 30 b of the CMOS chip 20, and the germanium layer 32film-formed on the aluminum containing layer 31 is made up of aplurality of strip layer sections 35 and a plurality of branch layersections 36. More specifically, the germanium layer 32 is made up ofconcentric three strip layer sections 35 having an identical shape andthe plurality of branch layer sections 36 which branch from each sectionof a centrally positioned strip layer section 35 to both side at a rightangle. Thus, the MEMS chip 10 and the CMOS chip 20 can be bonded withhigher sealing characteristics and bonding strength.

Referring to FIGS. 9A to 9C, the other embodiment (second embodiment) ofthe invention will be explained. Portions different from those of theabove embodiment will be mainly explained and same numerals are labeledfor similar elements. As illustrated in FIGS. 9A and 9B, the aluminumcontaining layer 31 film-formed on the bonding section 30 b of the CMOSchip 20 is made up of a plurality of aluminum ring-shaped layer sections37. The plurality of aluminum ring-shaped layer sections 37 are formedin a ring shape in a plan view concentrically with the bonding section30 b, and are disposed to be orthogonal in the inner/outer direction ofthe bonding section 30 b. Further, a plurality of ring-shaped germaniumlayers 32 (germanium ring-shaped layer sections 38) are film-formed soas to fill in space of these aluminum ring-shaped layer sections 37. Inthis case, the plurality of germanium ring-shaped layer sections 38 arefilm-formed to contact contact-ends of the plurality of aluminumring-shaped layer sections 37 in a vertical direction and to slightlyoverlap thereon (overlap layer sections 40) in a horizontal direction.

While, as illustrated in FIG. 9B, a plurality of engraved pits 41 areformed on the bonding section 30 a of the substrate 11. The plurality ofpits 41 are formed to correspond to positions (the overlap layersections 40) where the plurality of germanium ring-shaped layer sections38 overlap on the plurality of aluminum ring-shaped layer sections 38,and an alloy in a melting state after being heated and pressurized getsinto the plurality of pits 41. The plurality of pits 41 may be newlyformed on the substrate 11 after the sensing section 12 has been formed,or engraved portions formed in the formation process of the sensingsection 12 may be used. Further, the pits 41 may have intermittentaperture shape or consecutive groove shape.

FIG. 9C illustrates the bonding section after eutectic bonding. Aeutectic alloy in a melting state formed by heating spreads into theplurality of pits 41 thoroughly by capillary action in vacuum bypressurization. Then, the fixed eutectic alloy layer 33 is formed tobite into the bonding section 30 (substrate 11) of the MEMS chip 10. Inother words, as illustrated, since the eutectic alloy layer 33 is formedvertically with respect to a surface direction of the bonding section,bonding with higher bonding strength can be achieved.

According to the structures, a semiconductor substrate can be bondedwith high bonding strength and sealing characteristics at appropriateportions while adverse effect on the sensing section 12 is restrained.Further, such effective bonding enables the sensing section 12, theintegrated circuit 22 and the external circuit to conduct electrically,and high precision MEMS devices in which the sensing section 12 and thecircuit central section 23 are integrally packaged can be provided whilean external atmosphere such as moisture, temperature, dust and the likeis avoided.

In the embodiment, the silicon wafers formed with the sensing section 12and the integrated circuit 22 controlling the sensing section is used,but structures formed in the silicon wafer may be any circuits, notbeing limited thereto. Still further, a semiconductor substrate(composite semiconductor) having other base material instead of siliconwafer formed by silicon may be used. It is preferable that either one ofthe bonded semiconductor substrates have aluminum wirings.

REFERENCE NUMERALS

-   -   1 MEMS device 10 MEMS chip 12 sensing section 11, 12 substrate        20 CMOS chip 22 integrated circuit 31 aluminum containing layer        31 a, 32 a outer end 32 germanium layer 35 strip layer section        36 branch layer section 41 pit

What is claimed is:
 1. A method of bonding a semiconductor substrate,comprising: bonding a first semiconductor substrate with a secondsemiconductor substrate by eutectic bonding with pressurization andheating, an aluminum containing layer primarily made of aluminum and agermanium layer in an overlaid state being interposed between a bondingsurface of the first semiconductor substrate and a bonding surface ofthe second semiconductor substrate; film-forming the aluminum containinglayer on the bonding surface of the second semiconductor substrate andfilm-forming the germanium layer on the aluminum containing layer;receding an outer end of the germanium layer inward with respect to anouter end of the aluminum containing layer as to the aluminum containinglayer and the germanium layer in the overlaid state; and broadening apattern width of the aluminum containing layer than a pattern width ofthe germanium layer.
 2. The method of bonding a semiconductor substrateaccording to claim 1, wherein heating temperature and heating time ofthe pressurization and heating is controlled for alloying the germaniumlayer and the aluminum containing layer by eutectic bonding except anouter end portion of the aluminum containing layer.
 3. The method ofbonding a semiconductor substrate according to claim 1, wherein thealuminum containing layer and the germanium layer are film-formed oneither the first semiconductor substrate or the second semiconductorsubstrate.
 4. The method of bonding a semiconductor substrate accordingto claim 3, wherein the aluminum containing layer is film-formed in aring shape in planar view as having predetermined width, and thegermanium layer has one or more strip layer sections film-formed in aring shape in planar view on the aluminum containing layer.
 5. Themethod of bonding a semiconductor substrate according to claim 3,wherein the aluminum containing layer is film-formed in a ring shape inplanar view as having predetermined width, and the germanium layer has astrip layer section film-formed in a ring shape in planar view and aplurality of branch layer sections branched from the strip layer sectionon the aluminum containing layer.
 6. The method of bonding asemiconductor substrate according to claim 3, wherein the aluminumcontaining layer and the germanium layer are film-formed on the secondsemiconductor substrate and a pit is formed in the bonding surface ofthe first semiconductor substrate, in which a eutectic alloy generatedby the pressurization and heating fills.
 7. A MEMS device bonded by themethod of bonding a semiconductor substrate according to claim 1,wherein the first semiconductor substrate has a MEMS structure formed tobe engraved at the bonding surface side thereof, and the secondsemiconductor substrate has an integrated circuit formed at the bondingsurface side to control the MEMS structure.
 8. The MEMS device accordingto claim 7, wherein the MEMS device is either one of an accelerationsensor, an angular velocity sensor, an infrared ray sensor, a pressuresensor, a magnetic sensor or a sonic sensor.
 9. The method of bonding asemiconductor substrate according to claim 2, wherein the aluminumcontaining layer and the germanium layer are film-formed on either thefirst semiconductor substrate or the second semiconductor substrate. 10.The method of bonding a semiconductor substrate according to claim 9,wherein the aluminum containing layer is film-formed in a ring shape inplanar view as having predetermined width, and the germanium layer hasone or more strip layer sections film-formed in a ring shape in planarview on the aluminum containing layer.
 11. The method of bonding asemiconductor substrate according to claim 9, wherein the aluminumcontaining layer is film-formed in a ring shape in planar view as havingpredetermined width, and the germanium layer has a strip layer sectionfilm-formed in a ring shape in planar view and a plurality of branchlayer sections branched from the strip layer section on the aluminumcontaining layer.
 12. The method of bonding a semiconductor substrateaccording to claim 9, wherein the aluminum containing layer and thegermanium layer are film-formed on the second semiconductor substrateand a pit is formed in the bonding surface of the first semiconductorsubstrate, in which a eutectic alloy generated by the pressurization andheating fills.
 13. The method of bonding a semiconductor substrateaccording to claim 4, wherein the aluminum containing layer and thegermanium layer are film-formed on the second semiconductor substrateand a pit is formed in the bonding surface of the first semiconductorsubstrate, in which a eutectic alloy generated by the pressurization andheating fills.
 14. The method of bonding a semiconductor substrateaccording to claim 5, wherein the aluminum containing layer and thegermanium layer are film-formed on the second semiconductor substrateand a pit is formed in the bonding surface of the first semiconductorsubstrate, in which a eutectic alloy generated by the pressurization andheating fills.
 15. The method of bonding a semiconductor substrateaccording to claim 1, wherein a the weight ratio of the germanium layerto the aluminum containing layer is between 27 wt % and 57 wt %, and asealing ratio of a bonding section after the eutectic bonding is equalto or more than about 50%.
 16. The method of bonding a semiconductorsubstrate according to claim 1, wherein a bonding strength of a bondingsection after the eutectic bonding is equal to or more than about 30 Nwhen a weight ratio of the germanium layer to the aluminum containinglayer is between 27 wt % and 52 wt %.
 17. The method of bonding asemiconductor substrate according to claim 1, wherein a weight ratio ofthe germanium layer to the aluminum containing layer is between 33 wt %and 42 wt %, a sealing ratio is 100% and a bonding strength is between41.6 N and 56.3 N.
 18. The method of bonding a semiconductor substrateaccording to claim 1, wherein a weight ratio of the germanium layer tothe aluminum containing layer is between 33 wt % and 42 wt %.
 19. Themethod of bonding a semiconductor substrate according to claim 1,wherein the aluminum containing layer has a thickness of 800 nm and thegermanium layer has a thickness of 200 nm to 300 nm.